Field of Invention
The present invention relates to systems and methods for substrate processing, and more particularly to a method and system for Photo-sensitized Chemically Amplified Resist (PS-CAR) model calibration.
Description of Related Art
In lithographic patterning of semiconductor devices, shrinking technology nodes, and thus feature sizes are driving wavelengths into the extreme ultraviolet (EUV) range. At this time, EUV light sources are still under active development, and currently are not capable of developing and delivering the levels of illumination of prior generations of light sources. To address these shortcomings and still be able to utilize the current generation of EUV light sources, a resist chemistry and associated methods have been developed, called Photo-Sensitized Chemically-Amplified resist (PS-CAR). PS-CAR, like traditional Chemically-Amplified resist (CAR), utilizes acid generated within the resist feature for deprotection, but acid is generated in a two-step illumination process, unlike CAR where only a single patterned exposure is used.
In PS-CAR, a first patterned exposure is used, often at EUV frequencies, to generate a pattern (latent image within the resist) with a relatively small amount of generated acid, and at the same time generate a photosensitizer (PS) compound, for example from a photosensitizer generator added to the PS-CAR resist. Both the acid and photosensitizer (PS) are generated only in illuminated portions of the PS-CAR resist, during the first patterned exposure. Thereafter, a flood exposure is performed, i.e. with no pattern, at a second wavelength of light different than the wavelength of the first paterned exposure. The PS-CAR resist chemistry is chosen such that the photosensitizer (PS) is sensitive to the second wavelength of light used in the second flood exposure, while other resist components are not. The photosensitizer (PS), wherever present in the pattern formed during the first EUV patterned exposure causes further generation of acid during the flood exposure, with tenfold increases of acid concentration, for example, being possible. This photosensitizer-induced acid concentration increase results in greatly increased contrast, which allows more process latitude particularly with respect to the RLS tradeoff (Resolution—Line Width Roughness—Sensitivity). Thus, PS-CAR presents an enabling technology for EUV lithography because it allows the productive use of EUV sources and lithography at their present power levels.
It should be noted here that PS-CAR processes may involve additional steps, for example between the EUV patterned exposure and the flood exposure. The above description was simplified for purposes of clarity. Also, in some PS-CAR chemistry embodiments, no acid may be generated during the first EUV patterned exposure, and only photosensitizer may be generated, which generated photosensitizer causes generation of all acid during the flood exposure. Alternatively yet, acid may be generated in small quantities, as explained before, but it may be effectively consumed by competing chemical reactions, such as quenching events (depending on the amount of quencher present in the PS-CAR resist).
PS-CAR resist deposition, dosing, patterning, and developing may be highly sensitive processes in some embodiments. Due to the complexity of PS-CAR resist chemistries, and the scale of patterned features, many variables may contribute to the quality of the resist mask, and therefore, the resulting etched features. Resist patterning models have been used to predict resist layer and pattern qualities and to fine tune resist processing parameters, however none of the traditional models are suitable for patterning PS-CAR for a variety of reasons. First, PS-CAR resist processing flows include additional steps which are not required in traditional CAR resist flows. Previous models do not account for these additional flow steps. Second, PS-CAR resist is more sensitive to EUV and UV exposure dosing than traditional CAR resist, and prior models do not account for such sensitivities. Third, traditional models are designed with preset parameters tuned to the chemistry of traditional CAR chemistries, not for PS-CAR chemistries. One of ordinary skill will recognize a variety of additional shortcomings of prior models used for simulation traditional CAR resists.